Fig. 3

a 512 × 512 synthetic grid image with grids of dimensions 23 ×23 pixels, bounded by 8 pixels thick white lines. The red horizontal line represents the cross-sectional cut used to estimate the errors shown in Fig. 4 a and b. Imposed displacement field: b d ^u(x,y), the x component and c d ^v(x,y), the y component, as described by Eqs. (5) and (6). The minimum and maximum values of |d _u | are 0 & 11 pixels, respectively; the corresponding values for |d _v | are 0 & 9 pixels